HR: 0800h
AN: PP51E-0644    [Abstracts]
TI: Mid-Holocene Attenuation of ENSO From Oxygen-Isotopic Distributions of Individual Foraminifera
AU: * Olive, G C
EM: gco2101@columbia.edu
AF: Columbia University, 2960 Broadway, New York, NY 10027 United States
AU: Koutavas, A
EM: koutavas@mail.csi.cuny.edu
AF: Department of Engineering Science and Physics, College of Staten Island, The City University of New York, 2800 Victory Blvd, Staten Island, NY 10314 United States
AU: Ryan, W B
EM: billr@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AB: A growing number of climate reconstructions suggest that ENSO was attenuated during the mid-Holocene (~8 to 4 ky BP), and climate modeling indicates that this was a consequence of the altered orbital configuration mainly due to Earth's precession. However, this "weak ENSO" model suffers from near-total absence of marine observations from the central and eastern equatorial Pacific, the center of action of the ENSO system. Here we present results from oxygen-isotopic analysis of individual specimens of the surface dwelling foraminifer Globigerinoides ruber (white) isolated from narrow (~100 yr) sediment intervals of core V21-30 near the Galapagos Islands. These measurements are used to characterize the δ¹⁸O distribution of G. ruber populations within each interval, and to detect the presence of extreme hydrographic events associated with ENSO. Late Holocene samples reveal surprisingly broad δ¹⁸O distributions with a total range of 2.5 per mil, indicative of a wide tolerance of G. ruber to sea surface temperature and salinity, and ability to grow not only through the large annual cycle but also during extreme warm and cold ENSO episodes. By comparison, samples of mid-Holocene age have δ¹⁸O distributions which are generally narrower, both in terms of overall range and total variance. On a sample-by-sample basis, the mid-Holocene data reveal reductions of intra-species δ¹⁸O variance that are in most cases statistically significant at the 90 to 99% confidence level. When the full dataset is reduced to two separate groups representing the late and mid-Holocene, the observed change in variance is in the range of 40-66% and is significant at >99%. Subject to the caveat that these data represent only narrow sub-samples of the broader mid- and late Holocene periods, they are consistent with a frequency and/or amplitude attenuation of mid-Holocene ENSO. More generally, these results highlight the potential of individual foraminiferal analyses for reconstructing seasonal and interannual aspects of climate variability.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4922 El Nino (4522)
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005